Decelerometer



Sept. l2, 1950 D. E. HUDSON ErAL DECELEROMETER 4 Sheets-Sheet `1 Filed Oct. 24, 1945 l FIG. l

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DECELEROUETER 4 Sheets-Sheet' Filed Oct. 24,11945 mvENToRs FREMY/CK 6. L//YDVALL DONALD E. HUDSON ATTORNEY Sept. l2, 1950 Filed Oc-t. 24, 1945 D. E. HUDsQN Erm. 2,521,918

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INVENTORS meuse/ox c. wol/ALL Patented Sept. 12, 1950 UNITED STATES DECELEROMETER Donald E. Hudson, Pasadena, and Frederick C.

Lindvall,

Altadena, Calif., assignors to the United States of America as represented by the Secretary of the Navy Application Qctober 24, i945, Serial No. 624,294

1 Claim.

l This invention relates to instruments for measuring the deceleration of moving bodies and, particularly, to decelerometers for measuring the rate of change of velocity of projectiles,

. bombs, torpedoes, and the` like upon impact with water or solid objects.

When an ordnance missile strikes its target or some dense medium, such as water, through which it must pass to reach the target, the deceleration accompanying the impact imposes a great mechanical strain upon the body of the missile as well as upon its internal components. The hull of an aircraft torpedo, for example, must be constructed strongly enough to withstand water impacts without becoming clistorted; likewise, the engine used to propel the aircraft torpedo through the water must be sturdy in its design and secure in its mounting to prevent any undesirable displacement thereof or of any of its components due to deceleration forces set up by water impacts.

It can be readily seen that a factor which greatly influences the design of an ordnance missile is the deceleration it will be expected to encounter in its normal use. While the deceleration in any particular case can be found by several known empirical methods, the values arrived at by these methods are only rough approximations at best, and designs based on such values may suler as a consequence. It is to the improvement of methods of measuring the deceleration of ordnance missiles on impact with various targets that the present invention is particularly addressed.

Accordingly, a primary object of this invention is to provide an instrument capable of measuring the deceleration accompanying the force of impact of an ordnance missile upon water or solid objects.

Another object of the invention is to provide a decelerometer which will measure true values of deceleration of a moving body, notwithstanding the occurrence of deceleration components perpendicular to the axis along which the deceleration is measured.

A further object of the invention is to provide a decelerometer capable of furnishing permanent photographic records of the decelerations measured.

Other and ancillary objects and advantages will become apparent from a study of the accompanying specifications and drawings in which:

Fig. l is a perspective view of a partially disassembled decelerometer representing a preierred embodiment of our invention;

Fig. 2 is a plan view of the body portion of the decelerometer with one-half of the cap broken away;

Fig. 3 is a half-sectional, half-elevational view taken along line 3-3 of Fig. 2;

Fig. 4 is a sectional view takenalong line I--I of Fig. 2;

Fig. 5 is a bottom view of the body portion of the decelerometer;

Fig. 6 is a perspective view of the spider spring and weight members shown in section in Fig. 4: also illustrated. diagrammatically, is one of the electrical circuits employed in the decelerometer.

Fig. 'I is a sectional view of the recording camera employed with the decelerometer of the invention;

Fig. 8 is a plan view of the recording camera with the cover removed;

Figs. 9 and l0 are illustrations of typical photographic records obtained by the decelerometer.

Referring now particularly to Figs. 1, 2, 3, and 4, it is seen that the decelerometer body comprises two thick juxtaposed discs III and II containing complementing channels, which define chambers I2 and partition I3. A spider spring I4, shown in detail in Fig. 6, comprising a central web I6 and laterally extending cantilever spring arms I'I, is clamped by its central web between the two coacting halves of partition I3. The spring arms I'I which project into the chambers I2, carry electrical conducting weight members I8 positioned for engagement with a corresponding number of contact screws I9. The latter are threadably mounted to disc I0 but electrically insulated therefrom by suitable insulators 20. In addition to functioning as electrical contacts, screws I9 are adjustable to exert a predetermined load upon weight members I8, therebyl setting up a restoring force in spring arms I'I which are distorted by such load, thus permitting theconditions in which the several weight members I8 are separable from their corresponding contact screws under diierent and predetermnable forces. The utility of this arrangement will appear hereinafter when the operation of our decelerometer is discussed.

The disc II which constitutes the lower body member of the decelerometer is secured to a base plate 2|. Arresting bolts 22 project into chambers I2 through clearance holes 23; one such bolt terminates in proximity of, but not normally engaging, each of the respective weight members I8. djustment nuts 24 are provided to maintain the arresting bolts 22 in their proximate positions in relation to weight members I3.

Electrical circuits 26, one of which is shown graphically in Fig. 6, connect each of the respective contact screws I9 with a light source 21. All such electrical circuits 26 are connected in parallel with an electrical power supply 23 and a common ground post 29 and each is energized as long as its contact screw I9 and weight mem ber I8 are in engagement. Contact screws I! and ground posts 29 are connected to their circuits 26 by means of terminals 30 and 3| respectively. The entire decelerometer assembly is enclosed in a case 32 provided with a cover 22.

Calibration of the spring arms to determine the force required to break contact between weight members I8 and contact screws I9 is accomplished in the following manner. Base plate 2I is detached from disc Il; this operation likewise removes arresting bolts 22 from their positions adjacent weight members I8. A small screw (not shown) is then threaded into the tapped socket 34 which is provided in each of the Weight members I8, and a balance pan is suspended therefrom. These operations are, of course, performed individually for each spring, and the desired weight, representing the deceleration necessary to break contact between the weight member I8 and its contact screw I! is placed in the balance pan, and contact screw I9 is adjusted until it just breaks contact with the weight member I8.

Reference is now made additionally to Figs. 'I and 8. The camera shown generally at 38 comprises essentially a motor 31 for moving photographic film 38, an optical system 39 and mirrors 44 and 4|. The light sources 21 are arranged in an evenly spaced row transversely of the case in such manner that light from each may be trained on the 111m in the form of a spot, and formed into a trace by the movement of the film, each trace occupying its own lm area. An additional single light source 42 capable of furnishing a uniformly interrupted beam of light is also included in the camera case. An example of such an interrupted light source suitable for use with our decelerometer is the "Strobotron stroboscope controlled by a multivibrator described on page 531 of Theory and Applications of Electron Tubes," Second Edition, by Herbert J. Reich, published by McGraw-Hill Book Company, Inc. Frequencies of the multivibrator should be of the order of 100 cycles per second. A small orice 43 directs the light rays from each light source 21 to the mirror 4I, whence they are reected and directed through the optical system 39 to moving photographic film 38. In like manner, slit 44 directs the interrupted light rays from light source 42 to the photographic nlm 38 by means of mirrors 49 and 4I and optical system 39.

In Figs. 9 and 10 the films 48 there depicted represent actual records obtained in deceleration tests on aircraft torpedoes using the decelerometers of the present invention. The fine longitudinal lines 41 on the films are traces of the several light sources 21 from three decelerometers disposed parallel to the three axes of the aircraft torpedo. The discontinuities, as 48, in these lines resulted from de-energization of the electrical circuits 26 by movement of the weight members I8 away from contact screws I 9 under deceleration. Transverse lines 49 were recorded by the interrupted light rays from light source 42 and provide a ready and accurate means for measuring the length of time during which electrical circuits 2i are de-energized.

Operation of the decelerometer will now be described as it may be used to measure the deceleration of an aircraft torpedo upon impact with the water. Each contact screw I 2 is made to engage its corresponding weight member I8 and the spring arms I1 are calibrated as previously described. When the torpedo is released, both light sources 21 and 42 are energized; at the same time, electric motor I1 begins to operate. causing photographic iilm 38 to move past optical system 39 for exposure. As long as the torpedo is falling freely, all contact screws Il are in engagement with weight members Il, thereby maintaining electrical circuits 28 in a closed condition and permitting light sources 21 to function. Light source 42 functions independently of circuits 2l. Traces of light sources 21 and periodic transverse lines 48 corresponding to the intermittent ilashes of light source 42 are thus recorded on the moving film Il.

As the torpedo decelerates upon water impact, weight members I8, moving relative to the torpedo under their own inertia, break contact with screws I9, de-energizing electrical circuits 2l in sequence according to the tension placed on the several spring arms I1 by the contact screws Il. If the deceleration is great these circuits may be broken virtually simultaneously, but, thereafter, as the deceleration is decreased the contacts will close in the order determined by the tension in spring arms I1. The points on the photographic 111m at which the several electrical circuits are opened and closed furnish the data from which the deceleration may be computed.

While what has been described is particularly illustrative of a presently preferred embodiment of our invention, it is not intended that the scope of the invention be limited thereto but that it embrace any modiiications and changes which fall within the true spirit of the invention, as covered by the claim, occurring to those skilled in the art.

We claim:

A decelerometer comprising a pair of body members dening confronting channels separated by mating ridges, a spider spring including a web portion clamped between said ridges, cantilever springs extending laterally from said web portion into said channels, weights carried by the free ends of said springs, adjustable means for applying loads on said springs in addition to said weights, and meam for detecting movement of said springs beyond their deiiections as determined by said weights and said adjustable load applying means.

DONALD E. HUDSON. FREDERICK C. LINDVALL.

" file of this patent:

UNITED STATES PATEN IS Number Name Date 1,397,525 Kennedy Nov. 22, 1921 1,519,473 Zahm Dec. 16, 1924 1,787,940 Garbutt Jan. 6, 1931 1,921,833 McGorum Aug.'8, 1933 1,970,483 Alden Aug. 14, 1934 2,053,436 Knowles sept. 8, 1936 2,120,703 Janes June 14, 1938 2,237,326 Barry Apr. 8, 1941 2,283,180 Buchanan May 19, 1942 FOREIGN PATENTS Number Country Dgtg 637,939 France Feb. 13, 1928 

